In recent years, attention has been paid to small-sized fuel cells. In particular, a direct methanol fuel cell (hereinafter referred to as “DMFC”), which uses methanol as fuel, is regarded as promising, since the size can be reduced and the handling of fuel is easy.
The DMFC includes a membrane electrode assembly (hereinafter “MEA”) which is configured such that an electrolyte membrane is sandwiched between an anode and a cathode. In the anode of the DMFC, introduced methanol is oxidized and decomposed, and protons, electrons and carbon dioxide are produced. On the other hand, in the cathode, water is produced by a reaction between oxygen in the air, protons which have moved from the anode side, and electrons which are supplied from the anode via an external circuit. In addition, electric power is supplied by the electrons which flow through the external circuit.
As regards the DMFC, there is disclosed a structure wherein end portions of the MEA are inclined in the direction of stacking of layers in order to prevent short-circuit between the anode and the cathode. In addition, there is disclosed a structure wherein stepped portions in the direction of stacking of layers are formed at edge portions of a gas diffusion layer coupling body, and a protection film is coated on the stepped portions with such a thickness as to fill the stepped portions, thereby to prevent degradation of capability due to non-uniformity in surface-pressure distribution.
In the meantime, a voltage which is generated by the DMFC is lower than an ordinary cell, and is 1.21 V in cell voltage with no reversible loss. Thus, in the DMFC, such a method is adopted that a plurality of unit cells are laid over or arranged, and the unit cells are connected in series to increase a voltage. In particular, as regards a fuel cell which is required to occupy a smaller space, in many cases, plural unit cells are arranged in parallel and are connected in series by coupling anodes and cathodes by electrodes of a metal conductor.
However, in the case of arranging plural unit cells in parallel, there is a concern that neighboring anodes or cathodes are short-circuited by a catalyst falling from an anode catalyst layer or a cathode catalyst layer, and a predetermined voltage cannot be secured.